Balls filled with air under pressure, including soccer balls, basketballs inflated to between 7.5 and 8.5 psig (0.53-0.60 kg/cm2), footballs, volleyballs inflated to between 4 and 6 psig (0.28-0.42 kg/cm2) and beach balls, all of which have non-elastic shells, are of course well known, and those for designated sports must not be over-inflated. Some known play balls, especially play balls for young children, have elastomeric shells, formed for example of natural and artificial rubbers, polyvinyl chloride (PVC) plastic, or in some cases even of other plastics having the desirable of properties of flexibility and resilience.
For some types of known balls, it is desirable that such balls have a capacity to bounce, and it is known that balls bounce more when inflated to a greater pressure. However inflation pressures are limited due to the requirements of the sport in question, or due to the inability of the shell material to avoid rupture at elevated pressures.
Solid balls of a relatively small diameter, i.e. up to about 5 cm or so, generally referred to as super balls and made of polybutadiene, have an exceptional ability to bounce to a much greater degree than any known air filled balls (see Stingley U.S. Pat. No. 3,241,834). Such super balls are limited in size because, if larger than about 3 cm or so, they become too heavy for normal play, and can impose a danger to children. It would be desirable if a hollow ball could be created which would have the bouncing capacity of a super ball.
In recent years, shoes and particularly athletic shoes have been developed in which the soles and/or heels contain either mechanical springs or air so as to provide such shoes with more cushion and “bounce” than regular shoes. Many of these constructions are highly complex, e.g. see Peng U.S. Pat. No. 4,680,876, Kilgore et al U.S. Pat. No. 5,343,639, and McMahon et al U.S. Pat. No. 4,342,158. However, the degree of bounce in such shoe soles is greatly limited.